WDPS31 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11P (DOVI) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.3S 168.9E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 160 NM SOUTH-SOUTHEAST OF PORT VILA,
VANUATU
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES THAT
TC 11P CONTINUES TO SLOWLY CONSOLIDATE, ORGANIZE AND STRENGTHEN.
ANIMATED RADAR DATA FROM NEW CALEDONIA SHOWS WELL DEFINED LOW LEVEL
RAINBANDS WRAPPING INTO A RAGGED LOW LEVEL CIRCULATION CENTER
(LLCC). AND A 091725Z SSMIS 37GHZ MICROWAVE IMAGE DEPICTS A WEAK
LOW EMISSIVITY REGION OR NASCENT MICROWAVE EYE FEATURE, WHICH
ALIGNS WELL WITH THE RADAR INDICATED CENTER. BASED ON THE ABOVE
DATA, THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE. THE
INITIAL INTENSITY OF 45 KNOTS IS ASSESSED MEDIUM CONFIDENCE BASED
ON THE PGTW AND NFFN  DVORAK CURRENT INTENSITY ESTIMATES OF T3.0,
SLIGHTLY BELOW THE CIMSS ADT ESTIMATE OF T3.2 IN LIGHT OF AN AIDT
ESTIMATE OF 41 KNOTS. THE OVERALL ENVIRONMENT REMAINS FAVORABLE.
THE CIMSS SHEAR ANALYSIS INDICATES 16 KNOTS OF EASTERLY SHEAR,
THOUGH MODEL DERIVED SKEW-T'S INDICATE SHEAR MORE IN THE 10-13 KNOT
RANGE, AND ANIMATED WATER VAPOR IMAGERY SUGGESTS THE UPPER-LEVEL
OUTFLOW IS PUSHING OUT AGAINST THE EASTERLY SHEAR. JTWC UPPER-LEVEL
WIND ANALYSIS REVEALS A SMALL POINT SOURCE NEAR THE LLCC, PROVIDING
GOOD RADIAL OUTFLOW WITH SOME WEAK POLEWARD OUTFLOW. THE SYSTEM HAS
NOW BEGUN A SOUTHWESTWARD JOG AS THE SUBTROPICAL RIDGE (STR) TO THE
EAST HAS BECOME THE DOMINANT STEERING MECHANISM.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   PHFO: T2.5 - 35 KTS
   NFFN: T3.0 - 45 KTS
   CIMSS ADT: 49 KTS AT 091740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES IN
THE FORECAST TRACK OR INTENSITY, HOWEVER THE TRANSITION TYPE IS
CHANGED FROM SUBTROPICAL TO EXTRATROPICAL. 

FORECAST DISCUSSION: NOW THAT THE STR HAS ASSUMED THE PRIMARY
STEERING ROLE, TC 11P HAS STARTED A TURN TO THE SOUTHWEST BASED ON
ANIMATED RADAR DATA. THE SYSTEM IS FORECAST TO CONTINUE TRACKING
SOUTHWESTWARD THROUGH THE FIRST 24 HOURS OF THE FORECAST, CROSSING
OVER OR VERY NEAR THE SOUTHEASTERN TIP OF NEW CALEDONIA BEFORE TAU
24. AFTER PASSING THE ISLANDS THE SYSTEM WILL GRADUALLY TURN MORE
SOUTHWARD AS IT ROUNDS THE RIDGE AXIS, AND EVENTUALLY TURN
SOUTHEASTWARD TOWARDS NEW ZEALAND AFTER TAU 72. AS THE WEDGE OF DRY
AIR THAT WAS PREVIOUSLY ANALYZED TO BE WRAPPING INTO THE CENTER HAS
WEAKENED AND MOISTENED, THE SYSTEM HAS STEADILY BEGUN TO ORGANIZE.
THIS TREND IS ANTICIPATED TO CONTINUE AND ACCELERATE AS THE SHEAR
IS FORECAST TO GENERALLY SLACKEN OVER THE NEXT 12 HOURS OR SO. SSTS
REMAIN AT OR ABOVE 26C FOR THE NEXT 36 HOURS, AND THUS THE SYSTEM
IS FORECAST TO STEADILY INTENSITY TO A PEAK OF 70 KNOTS BY TAU 36.
BAY TAU 48 THE SYSTEM WILL MOVE ACROSS A SHARP SST GRADIENT TO
WATERS LESS THAN 23C AND BEGIN TO INTERACT WITH AN APPROACHING
MAJOR SHORTWAVE TROUGH, MARKING THE BEGINNING OF EXTRATROPICAL
TRANSITION. BY TAU 72, THE SYSTEM TRANSITIONS TO A STORM-FORCE
EXTRATROPICAL LOW AS IT WILL BE IN PHASE AND JUST AHEAD OF THE
UPPER-LEVEL TROUGH, MOVES UNDER A 200MB POLAR FRONT JET STREAK AND
DEVELOPS BAROCLINICITY.   

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH THE
FORECAST PERIOD, WITH AN 80NM SPREAD AT TAU 48, INCREASING TO 150NM
AT TAU 72, THOUGH THERE IS A MODEST AMOUNT OF ALONG-TRACK SPREAD
EVIDENT IN THE GUIDANCE AFTER TAU 48. THE JTWC TRACK HAS SHIFTED A
BIT TO THE WEST, OR RIGHT WHEN LOOKING DOWN TRACK, BASED ON THE
RECENT NEAR-TERM MOTION VECTOR. THE FORECAST REMAINS ON THE WEST
SIDE OF THE ENVELOPE THROUGH TAU 48, THEN MOVES CLOSER TO THE
CONSENSUS MEAN BY TAU 72, WITH HIGH CONFIDENCE. INTENSITY GUIDANCE
IS MIXED, WITH THE HWRF MARKING THE LOW END OF THE ENVELOPE,
PEAKING AT AROUND 55 KNOTS, WHILE THE DECAY SHIPS ARE THE MOST
BULLISH, PEAKING NEAR 75 KNOTS. THE JTWC FORECAST LIES ON THE HIGH
END OF THE ENVELOPE, ROUGHLY 10 KNOTS HIGHER THAN THE CONSENSUS
MEAN, THROUGH TAU 36 THEN SLIGHTLY BELOW THE MEAN THEREAFTER.
CONFIDENCE IN THE INTENSITY FORECAST IS MEDIUM DUE TO THE LARGE
UNCERTAINTIES IN THE GUIDANCE. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM//
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